Abstract
The objective of this project is to improve the prediction of engine knock by developing a new
combustion modeling framework. Engine knock is a limiting factor to constrain the increase of
fuel efficiency for spark ignition (SI) engines in most passenger cars. Efforts to increase fuel
efficiency, increasing the compression ratio or downsizing, lead to the increase in the tendency of
the knock occurrence. The knock is an undesired ignition of the end-gas, unburned fuel/air mixture
ahead of the spark-ignited premixed flame, resulting in rapid in-cylinder pressure rises and engine
damages.
The combustion modeling framework developed in this project can consider turbulence-chemistry
interactions during end-gas ignition, while using a reasonably detailed chemical mechanism developed
for ignition and combustion reactions under engine relevant conditions, and the subtle characteristics
of spark-ignited flame propagation. It is developed in the context of large eddy simulation
(LES), which can capture stochastic in-cylinder processes. The developed model is incorporated
into a commercial software for engine simulation, CONVERGE CFD, as a user defined function,
and validated. Engine knock and knock-free experiments as well as direct numerical simulation
(DNS) of end-gas ignition in homogeneous turbulence are performed to help model development
and provide data sets for model validation. With further validation, the developed model is expected
to advance the predictive capability for engine knock simulations and thus contribute to
improving the fuel efficiency.
